The present invention is directed to peptide analogues of glucagon-like peptide-1, the pharmaceutically-acceptable salts thereof, to methods of using such analogues to treat mammals and to pharmaceutical compositions useful therefor comprising said analogues.
Glucagon-like peptide-1 (7-36) amide (GLP-1) is synthesized in the intestinal L-cells by tissue-specific post-translational processing of the glucagon precursor preproglucagon (Varndell, J. M., et al., J. Histochem Cytochem, 1985:33:1080-6) and is released into the circulation in response to a meal. The plasma concentration of GLP-1 rises from a fasting level of approximately 15 pmol/L to a peak postprandial level of 40 pmol/L. It has been demonstrated that, for a given rise in plasma glucose concentration, the increase in plasma insulin is approximately threefold greater when glucose is administered orally compared with intravenously (Kreymann, B., et al., Lancet 1987:2, 1300-4). This alimentary enhancement of insulin release, known as the incretin effect, is primarily humoral and GLP-1 is now thought to be the most potent physiological incretin in humans. In addition to the insulinotropic effect, GLP-1 suppresses glucagon secretion, delays gastric emptying (Wettergren A., et al., Dig Dis Sci 1993:38:665-73) and may enhance peripheral glucose disposal (D'Alessio, D. A. et al., J. Clin Invest 1994:93:2293-6).
In 1994, the therapeutic potential of GLP-1 was suggested following the observation that a single subcutaneous (s/c) dose of GLP-1 could completely normalize postprandial glucose levels in patients with non-insulin-dependent diabetes mellitus (NIDDM) (Gutniak, M. K., et al., Diabetes Care 1994:17:1039-44). This effect was thought to be mediated both by increased insulin release and by a reduction in glucagon secretion. Furthermore, an intravenous infusion of GLP-1 has been shown to delay postprandial gastric emptying in patients with NIDDM (Williams, B., et al., J. Clin Endo Metab 1996:81:327-32). Unlike sulphonylureas, the insulinotropic action of GLP-1 is dependent on plasma glucose concentration (Holz, G. G. 4th, et al., Nature 1993:361:362-5). Thus, the loss of GLP-1-mediated insulin release at low plasma glucose concentration protects against severe hypoglycemia. This combination of actions gives GLP-1 unique potential therapeutic advantages over other agents currently used to treat NIDDM.
Numerous studies have shown that when given to healthy subjects, GLP-1 potently influences glycemic levels as well as insulin and glucagon concentrations (Orskov, C, Diabetologia 35:701-711, 1992; Holst, J. J., et al., Potential of GLP-1 in diabetes management in Glucagon III, Handbook of Experimental Pharmacology, Lefevbre P J, Ed. Berlin, Springer Verlag, 1996, p. 311-326), effects which are glucose dependent (Kreymann, B., et al., Lancet ii: 1300-1304, 1987; Weir, G. C., et al., Diabetes 38:338-342, 1989). Moreover, it is also effective in patients with diabetes (Gutniak, M., N. Engl J Med 226:1316-1322, 1992; Nathan, D. M., et al., Diabetes Care 15:270-276, 1992), normalizing blood glucose levels in type 2 diabetic subjects (Nauck, M. A., et al., Diagbetologia 36:741-744, 1993), and improving glycemic control in type 1 patients (Creutzfeldt, W. O., et al., Diabetes Care 19:580-586, 1996), raising the possibility of its use as a therapeutic agent.
GLP-1 is, however, metabolically unstable, having a plasma half-life (t1/2) of only 1-2 min in vivo. Exogenously administered GLP-1 is also rapidly degraded (Deacon, C. F., et al., Diabetes 44:1126-1131, 1995). This metabolic instability limits the therapeutic potential of native GLP-1.
A number of attempts have been taken to improve the therapeutic potential of GLP-1 and its analogs through improvements in formulation. For example, International patent publication no. WO 01/57084 describes a process for producing crystals of GLP-1 analogues which are said to be useful in the preparation of pharmaceutical compositions, such as injectable drugs, comprising the crystals and a pharmaceutical acceptable carrier. Heterogeneous micro crystalline clusters of GLP-1(7-37)OH have been grown from saline solutions and examined after crystal soaking treatment with zinc and/or m-cresol (Kim and Haren, Pharma. Res. Vol. 12 No. 11 (1995)). Crude crystalline suspensions of GLP(7-36)NH2 containing needle-like crystals and amorphous precipitation have been prepared from phosphate solutions containing zinc or protamine (Pridal, et. al., International Journal of Pharmaceutics Vol. 136, pp. 53-59 (1996)). European patent publication no. EP 0619322A2 describes the preparation of micro-crystalline forms of GLP-1 (7-37)OH by mixing solutions of the protein in pH 7-8.5 buffer with certain combinations of salts and low molecular weight polyethylene glycols (PEG). U.S. Pat. No. 6,566,490 describes seeding microcrystals of, inter alia, GLP-1 which are said to aid in the production of purified peptide products. U.S. Pat. No. 6,555,521 (US '521) discloses GLP-1 crystals having a tetragonal flat rod or a plate-like shape which are said to have improved purity and to exhibit extended in vivo activity. US '521 teaches that such crystals are relatively uniform and remain in suspension for a longer period of time than prior crystalline clusters and amorphous crystalline suspensions which were said to settle rapidly, aggregate or clump together, clog syringe needles and generally exacerbate unpredictable dosing.
A biodegradable triblock copolymer of poly [(dl-lactide-co-glycolide)-b-ethylene glycol-b-(-lactide-co-glycolide)] has been suggested for use in a controlled release formulation of GLP-1. However like other polymeric systems, the manufacture of triblock copolymer involves complex protocols and inconsistent particulate formation.
Similarly, biodegradable polymers, e.g., poly(lactic-co-glycolic acid) (PLGA), have also been suggested for use in sustained delivery formulations of peptides. However the use of such biodegradable polymers has been disfavored in the art since these polymers generally have poor solubility in water and require water-immiscible organic solvents, e.g., methylene chloride, and/or harsh preparation conditions during manufacture. Such organic solvents and/or harsh preparation conditions are considered to increase the risk of inducing conformational change of the peptide or protein of interest, resulting in decreased structural integrity and compromised biological activity. (Choi et al., Pharm. Research, Vol. 21, No. 5, (2004).) Poloxamers have been likewise faulted. (Id.)
The GLP-1 compositions described in the foregoing references are less than ideal for preparing pharmaceutical formulations of GLP's since they tend to trap impurities and/or are otherwise difficult to reproducibly manufacture and administer. Also, GLP analogs are known to induce nausea at elevated concentrations, thus there is a need to provide a sustained drug effect with reduced initial plasma concentrations. Hence, there is a need for GLP-1 formulations which are more easily and reliably manufactured, that are more easily and reproducibly administered to a patient, and that provide for reduced initial plasma concentrations in order to reduce or eliminate unwanted side-effects.